Applying New Diagnostics To Potato Cyst Nematodes

Published on 6 January 2010 in Sustainability and Communities , Climate, water and energy

Introduction

The potato cyst nematodes (PCN), Globodera rostochiensis and G. pallida, are a serious problem for potato growers in Scotland, in other areas of the UK and abroad. Continuing spread and difficulty in detecting low levels of new infestations; persistence of viable cysts in the soil for many years; increasing pressure to reduce the use of chemicals to control PCN; and limited availability of cultivars with full resistance, particularly for G. pallida, are some of the issues facing the potato industry.

Novel methods to control and prevent the spread of PCN are urgently needed to limit the economic losses from this pest to potato crops providing an alternative to long rotations and the use of nematicides. Workers at SCRI and SASA have teamed up to develop an improved molecular diagnostic for PCN using the latest technology.

This diagnostic assay will be used at SASA in their statutory duty to monitor PCN in Scotland and at SCRI to investigate how PCN reproduction is effected when the two species are combined on different potato genotypes and in temperatures to assess the impact that climate changes may have on PCN.

Key Points

• SCRI and SASA have worked together to develop a molecular assay for potato cyst nematodes using the latest technology.
• SASA will employ this assay to implement the new European Council Directive concerning PCN (2007/33/EC) which comes into force on 1 July 2010.
• The new molecular assay is being used to assess reproduction of the two species when in mixtures and on potato genotypes that combine different sources of resistance.
• The new molecular assay is being used to assess how PCN will respond to changes in the climate.

Figure 1: Damage to potato crop caused by potato cyst nematodes (copyright SASA)

 

Research Undertaken

The latest European Council Directive concerning PCN (2007/33/EC) comes into force on 1 July 2010 and will harmonise methods for monitoring and controlling the spread of PCN across the EU. The new soil sampling rate is 1500ml of soil /ha, with a reduced rate of 400ml of soil/ha applying to fields where there is a documented test history showing freedom from PCN, or where potatoes are grown in a rotation of one in seven years or longer. Further reductions can also apply for larger fields or where the field is situated in a pest free area.

For Scotland there will be a significant increase in the number of soil samples required to be examined each year. Currently a well established method using visual observation of the cysts and subsequent separation of Globodera pallida and G. rostochiensis based on a range of morphological characteristics is used however, it is no longer practicable to continue using this method and process sufficient samples prior to the start of planting.

A new testing method that can process very high numbers of soil samples whilst maintaining or improving the accuracy of the current test was needed. The new DNA based test not only provides the level of sensitivity and specificity required but can also handle large numbers of samples at a cost per sample that compares with the current test. It is also expected that there will be a significant improvement in sample turn-around enabling growers to make more timely crop management decisions.

In addition to the statutory uses of this new DNA test for PCN, there are other applications with relevance to the potato industry. PCN frequently occurs as mixed infestations in the UK but quantifying the contribution of each species to the infestation and to the disease process has up till now been tedious. Determining the relative proportion of each species of PCN before and after the potato crop using morphological differences to distinguish the two species of biochemical methods using individual cysts is extremely laborious.

With the new method both species can be accurately identified and quantified much more efficiently. The test will not only deal with a mixture of the two species but can be used to quantify the relative proportions. This allows questions about the interaction and competition between the two species to be considered in both experimental and field conditions. Such information can be then be used to inform management strategies.

Already the availability of the test has allowed glasshouse experiments designed to compare the reproduction of individual species with mixtures of the two on potato cultivars that are susceptible to both or one or the other of the two species. These experiments have shown that potato genotypes that combine resistances may be more effective when both species are present. This new DNA diagnostic assay is also being used in experiments which examine the reproduction of the two species of PCN on potatoes grown at different temperatures. This work will help us understand the consequences of changes in temperature and climate conditions on PCN infection and on whether the resistance that is available to control PCN is likely to be influenced by climate change.

Policy Implications

Food security is of major concern as the world population continues to increase and climate change brings uncertainty about production. Limiting crop losses from diseases and pests using sustainable practices and developing novel control methods is integral to stable food production. Potato cyst nematodes are a major disease of potatoes and their control through the use of nematicides has significant economic and environmental consequences.

Changes in the Scottish climate may exacerbate the effects of pests and diseases in the future so anticipating these changes and developing new control strategies which employ new technology is needed to maintain a successful agricultural sector in the Scottish economy as well as to support rural communities.

Author

Dr Vivian Blok, SCRI, Dr David Kenyon, SASA Vivian.Blok@scri.ac.uk; David.Kenyon@sasa.gsi.gov.uk

Topics

Sustainability and Communities , Climate, water and energy

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